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GENETICS AND HEREDITY. A trait is a notable feature or quality in a person. Each of us has a different combination of traits that make us unique. Traits are passed from generation to generation. We inherit traits from our parents, and we pass them on to our children .
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A trait is a notable feature or quality in a person. Each of us has a different combination of traits that make us unique. Traits are passed from generation to generation. We inherit traits from our parents, and we pass them on to our children. • Physical traits are characteristics of one’s physical makeup. These include hair color, eye color, and height.
Behavioral traits are characteristics of the way one acts. A sheepdog’s herding instinct and a retriever’s desire to fetch are good examples of behavioral traits. • Predispositions to medical conditions provide increased risk of getting a certain type of a disease. This is also a type of trait that can be passed from parent to child. Some examples of such diseases are sickle-cell anemia, cystic fibrosis, heart disease, cancer, and some types of mental illness.
Earlobe attachment: If earlobes hang free, they are detached. If they attach directly to the side of the head, they are attached ear lobes. Some scientists report that this trait is due to a single gene for which unattached earlobes is dominant and attached earlobes is recessive. Other scientists believe that this trait is probably due to multiple genes. The size and appearance of the lobes are inherited traits.
Tongue Rolling: In 1940, a famous geneticist noted that about 70% of people of European descent are able to roll up the lateral edges of the tongue, while the remaining 30% were unable to do so. Tongue rolling may be due to a single gene with the ability to roll the tongue a dominant trait and the lack of tongue rolling a recessive trait. • However, there is some question about the inheritance of tongue rolling because recent studies have shown that around 30% of identical twins do not share the trait.
CLEFT CHIN • This trait is reportedly due to a single gene with a cleft chin dominant and a smooth chin recessive.
DIMPLES • Dimples are reportedly due to a single gene with dimples dominant (people may exhibit a dimple on only one side of the face) and a lack of dimples recessive.
HANDEDNESS • Some scientists have reported that handedness is due to a single gene with right-handedness dominant and left-handedness recessive. However, other scientists have reported that the interaction of two genes is responsible for this trait.
FRECKLES • This trait is reportedly due to a single gene; the presence of freckles is dominant; the absence of freckles is recessive.
NATURALLY CURLY HAIR • Early geneticists reported that curly hair was dominant and straight hair was recessive. More recent studies suggest that more than one gene may be involved.
ALLERGIES • While allergic reactions are induced by things a person comes in contact with, such as dust, particular foods, and pollen, the tendency to have allergies is inherited. If a parent has allergies, there is a one in four (25%) chance that their child will also have allergy problems. This risk increases if both parents have allergies.
HAND CLASPING • Fold your hands together by interlocking your fingers without thinking about it. Which thumb is on top—your left or your right? • One study found that 55% of people place their left thumb on top. 45% place their right thumb on top and 1% have no preference. • A study of identical twins concluded that hand clasping has at least some genetic component.
COLOR BLINDNESS • Colorblindness is due to a recessive allele located on the X chromosome. Women have two X chromosomes, one of which usually carries the allele for normal color vision. Therefore, few women are colorblind. Men have only one X chromosome, so if they carry the allele for colorblindness, they will exhibit this trait. Thus, colorblindness is seen more frequently in men than in women.
HAIRLINE SHAPE • Hairline shape is reportedly due to a single gene with a widow’s peak dominant and a straight hairline recessive.
HITCHHIKER’S THUMB • Someone who has a thumb which bends backwards when extended is said to have a hitchhiker's thumb. This is a genetic trait, and it does not interfere with the thumb's normal functions. Hitchhiker's thumb is also not linked with any other genetic conditions; it is simply an interesting phenotype, akin to people who can curl their tongues. To see if you have a hitchhiker's thumb, make a fist and extend your thumb. If you notice a significant bend, you have inherited this trait. Hitchhiker's thumb is a recessive trait, which means that people must inherit the gene from both parents for it to manifest.
Gregor Mendel was an Austrian monk who experimented with pea plants in the mid-1800s. • He kept track of a number of traits over several generations, including: color of the seeds, plant height, whether the pod was smooth or wrinkled, and the shape of the seeds.
Over time, he noticed that certain plants produced new plants that were similar to the parents. For example, short "parent" plants produced more short plants, and tall "parent" plants have tall offspring. • When he bred plants with different traits, he found patterns in the appearance of the new plants. He concluded that some genes are dominant and other ones are recessive. Dominant genes hide other genes that are present, and the trait corresponding to that gene will appear. Traits represented by recessive genes will only appear when the dominant gene is not present.
Genes contain information about a specific characteristic or trait and can either be dominant or recessive. Genes are found on chromosomes, but not all copies of a gene are identical. The different form of a gene is called an allele. • Allelesare represented using capital letters (dominant) and lower case letters (recessive). When the alleles are identical, the individual is homozygous for that trait. If the pair is made of two different alleles, the individual is heterozygous.
A homozygous pair of can be either dominant (AA, BB) or recessive (aa, bb). Heterozygous pairs are made up of one dominant and one recessive allele (Aa, Bb). In heterozygous individuals only the dominant allele is expressed, while the other allele, the recessive, is hidden but still present. Capital letters represent dominant genes and lower case letters, recessive genes. • What does all this mean? Let’s look at an example: In rabbits, brown fur color is dominant over white fur color. We would represent a brown allele with an uppercase “B”. We would represent a white allele with a lowercase “b”.
If a baby bunny rabbit inherited two dominant alleles “BB”, his fur color would be brown. If the baby bunny rabbit inherited one dominant and one recessive allele “Bb”, his fur color would still be brown. This is because the dominant allele would cover up or hide the recessive allele. Finally, if the baby bunny rabbit inherited two recessive alleles “bb” he would have white fur. White fur would only be possible if no dominant allele was present
An organism’s appearance is known as its phenotype. • In bunny rabbits, possible phenotypes for the characteristic of fur color include brown, white, and black. Both inherited alleles together form an organism’s genotype. • Our baby rabbits with brown fur could have a genotype of either “BB” or “Bb”. Another of our baby rabbits may have white fur and their genotype would be expressed “bb”. • Phenotyperefers to the appearance or expression of the trait, and genotyperefers to the genetic make-up of the gene.
Remember: If you are asked for a phenotype, you should give a characteristic (brown or white). • If you are asked for a genotype, you should give an allele combination “bb” or “Bb” or “BB”.
PUNNETT SQUARES • The Punnett square is a diagram used to predict an outcome of a particular cross or breeding experiment. • Used by biologists to determine the probability of an offspring having a particular genotype or phenotype, the Punnett square is a summary of every possible combination of two maternal (mother) alleles with two paternal (father) alleles for each gene being studied in the cross.
The mathematical chance that something will happen is known as probability. Probability is usually written as a percentage or a ratio. When you toss a coin, there is a 50% chance of getting heads. In a parent with two different alleles, such as Pp, there is a 50% chance of offspring getting a "P" and a 50% chance of getting a "p".
In this example, the Dad rabbit is homozygous for grey fur and the mother is homozygous for brown fur. Each parent contributes one of their alleles to their offspring. • Because grey is dominant, their offspring will all be heterozygous for grey fur. • If we were asked for the genotypic probability or ratio, we would express it as 100% Bb or 4:4 Bb. • If we were asked for the phenotypic probability or ratio, we would express it as 100% grey or 4:4 grey.
YOU TRY IT! • Use a Punnett Square to predict the genotype and phenotype of the offspring in a cross between two heterozygous (hybrid) tall (Tt) pea plants. • In pea plants, yellow peas are dominant over green plants. Use a Punnett square to predict the phenotype and genotype of the offspring in a cross between a plant heterozygous/hybrid for yellow (Yy) peas and a plant homozygous/purebred for green (yy) peas.
In pea plants, yellow peas are dominant over green plants. Use a Punnett square to predict the phenotype and genotype of the offspring in a cross between two plants heterozygous/hybrid for yellow peas. • In pea plants, round peas are dominant over wrinkled peas. Use a Punnett square to predict the phenotype and genotype of the offspring in a cross between homozygous/purebred for round peas (RR) and a plant homozygous/purebred (rr) for wrinkled peas
In pea plants, round peas are dominant over wrinkled peas. Use a Punnett square to predict the phenotype and genotype of the offspring in a cross between two plants heterozygous/hybrid for round peas.
MEET MOM- MODEL A MEET DAD- MODEL B Red antennae 3 body segments Curly tail 2 pairs of legs Green nose Black feet Green eyes Green antennae 2 body segments Straight tail 3 pairs of legs Blue nose Green feet 2 eyes
BUG BABY PICTURE BUG BABY PICTURE
